This was only an issue with rounding. If your minion has less than 100 in ST or DX then some bonus will get rounded down for the minion and this rounding gets passed on to the familiar.

Example: 20 ST with +22 TG This will increase minion ST to 24.4 but because of the 0.4 can't get added, it rounds to 24. 24 is actually the same as a +20 TG and this gets brought over to the familiar in the form of ST benefit being based off of the difference between 24 vs 20. It gains a 30% increase instead of the normal 33%.

Say your familiar had 1m ST. The difference would be between 1.3 mil ST and 1.33 mil ST.

At 100 ST on the minion all bonuses are fully added. The same applies to DX